Global and local covert visual attention: Evidence from a bayesian hidden markov model

Psychological, psychophysical and physiological research indicates that people switch between two covert attention states, local and global attention, while visually exploring complex scenes. The focus in the local attention state is on specific aspects and details of the scene, and on examining its content with greater visual detail. The focus in the global attention state is on exploring the informative and perceptually salient areas of the scene, and possibly on integrating the information contained therein. The existence of these two visual attention states, their relative prevalence and sequence in time has remained empirically untested to date. To fill this gap, we develop a psychometric model of visual covert attention that extends recent work on hidden Markov models, and we test it using eye-movement data. The model aims to describe the observed time series of saccades typically collected in eye-movement research by assuming a latent Markov process, indicative of the brain switching between global and local covert attention. We allow subjects to be in either state while exploring a stimulus visually, and to switch between them an arbitrary number of times. We relax the no-memory-property of the Markov chain. The model that we develop is estimated with MCMC methodology and calibrated on eye-movement data collected in a study of consumers' attention to print advertisements in magazines.We thank Dominique Claessens of Verify International for making the data available to us.     

Changes in Saccadic and Manual Motor Control After Ocular Smooth Pursuit Adaptive Modifications

The gain of ocular smooth pursuit responses can be adaptively modified under certain circumstances. Evidence that these modifications are caused, at least partly, by changes at a sensory level comes from the fact that subsequent manual tracking movements generated during visual fixation are also modified in a similar manner. The question addressed in the present experiment was whether the modifications are constrained specifically to responses such as these, which are driven by retinal image motion, or whether they can also influence movements that make use of retinal image position. This was accomplished by comparing manual and oculomotor responses to step changes in target position before and after smooth pursuit adaptation. The results showed that, as with manual tracking movements, these responses were also modified by the adaptive procedure, although to a lesser extent. In particular, following a 20-min period in which subjects (N = 4) were submitted to a procedure designed to increase the gain of the smooth pursuit system, manual step tracking movements and ocular saccades displayed larger amplitudes than those shown prior to the adaptation. In addition, these gain changes were accompanied by appropriate alterations in response kinematics. Taken together, these results suggest that the mechanisms responsible for adaptive modifications in the smooth pursuit system are also able to more generally influence the processing of visuospatial information. The possible neurophysiological substrate underlying these mechanisms is discussed.     

The relationship between reward and probability: Evidence that exploration may be intrinsically rewarding

ABSTRACT

The probability of an event occurring and the reward associated with the event can both modulate behaviour. Response times are decreased to stimuli that are either more rewarding or more likely. These two factors can be combined to give an Expected Value (EV) associated with the event (i.e., probability of the event x reward magnitude). In four experiments we investigate the effect of reward and probability on both saccadic and manual responses. When tested separately we find evidence for both a reward and probability effect across response types. When manipulations of reward magnitude and probability of the event were combined, the probability modulations dominated and these data were not well accounted for by the EV. However, a post-hoc model that included an additional intrinsic reward associated with responding provided an excellent account for the data. We argue that reward consists of both an explicit and intrinsic component. In our task, the saccadic and manual responses are linked to the information provided by the targets and the goals of the task, and successful completion of these is in itself rewarding. As a result, targets associated with a higher probability of being presented have a higher intrinsic reward.     

Saccadic eye movements as indicators of cognitive function in older adults

Older adults appear to have greater difficulty ignoring distractions during day-to-day activities than younger adults. To assess these effects of age, the ability of adults aged between 50 and 80 years to ignore distracting stimuli was measured using the antisaccade and oculomotor capture tasks. In the antisaccade task, observers are instructed to look away from a visual cue, whereas in the oculomotor capture task, observers are instructed to look toward a colored singleton in the presence of a concurrent onset distractor. Index scores of the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) were compared with capture errors, and with prosaccade errors on the antisaccade task. A higher percentage of capture errors were made on the oculomotor capture tasks by the older members of the cohort compared to the younger members. There was a weak relationship between the attention index and capture errors, but the visuospatial/constructional index was the strongest predictor of prosaccade error rate in the antisaccade task. The saccade reaction times (SRTs) of correct initial saccades in the oculomotor capture task were poorly correlated with age, and with the neurospsychological tests, but prosaccade SRTs in both tasks moderately correlated with antisaccade error rate. These results were interpreted in terms of a competitive integration (or race) model. Any variable that reduces the strength of the top-down neural signal to produce a voluntary saccade, or that increases saccade speed, will enhance the likelihood that a reflexive saccade to a stimulus with an abrupt onset will occur.     

A predictive coding model of gaze shifts and the underlying neurophysiology

A comprehensive model of gaze control must account for a number of empirical observations at both the behavioural and neurophysiological levels. The computational model presented in this article can simulate the coordinated movements of the eye, head, and body required to perform horizontal gaze shifts. In doing so it reproduces the predictable relationships between the movements performed by these different degrees of freedom (DOFs) in the primate. The model also accounts for the saccadic undershoot that accompanies large gaze shifts in the biological visual system. It can also account for our perception of a stable external world despite frequent gaze shifts and the ability to perform accurate memory-guided and double-step saccades. The proposed model also simulates peri-saccadic compression: the mis-localization of a briefly presented visual stimulus towards the location that is the target for a saccade. At the neurophysiological level, the proposed model is consistent with the existence of cortical neurons tuned to the retinal, head-centred, body-centred, and world-centred locations of visual stimuli and cortical neurons that have gain-modulated responses to visual stimuli. Finally, the model also successfully accounts for peri-saccadic receptive field (RF) remapping which results in reduced responses to stimuli in the current RF location and an increased sensitivity to stimuli appearing at the location that will be occupied by the RF after the saccade. The proposed model thus offers a unified explanation for this seemingly diverse range of phenomena. Furthermore, as the proposed model is an implementation of the predictive coding theory, it offers a single computational explanation for these phenomena and relates gaze shifts to a wider framework for understanding cortical function.     

视觉搜索过程中的眼跳及其机制

该文对视觉搜索过程中的眼跳及其时间进程、神经机制及相关的理论与模型等方面研究进行了回顾。发现内外源性眼跳得到了研究者的普遍关注,对眼运动记忆、返回抑制及眼跳时间进程的研究尚存在分歧。关于眼跳的神经机制,额叶眼动区与上丘分别被认为是眼跳的关键区与指令发出者。尽管不同的眼跳理论与模型对眼跳现象给出了各自的解释,但都不尽完善,尚需对这些理论进行整合或者提出新的解释模型。文章还对未来的研究进行了展望     

Enhanced saccadic control in young people with Tourette syndrome despite slowed pro‐saccades

Tourette syndrome (TS) is a neurodevelopmental disorder characterized by motor and vocal tics. Tics are repetitive and uncontrolled behaviours that have been associated with basal ganglia dysfunction. We investigated saccadic eye movements in a group of young people with TS but without co‐morbid ADHD. Participants performed two tasks. One required them to perform only pro‐saccade responses (pure pro‐saccade task). The other involved shifting, unpredictably, between executing pro‐ and anti‐saccades (mixed saccade task). We show that in the mixing saccade task, the TS group makes significantly fewer errors than an age‐matched control group, while responding equally fast. By contrast, on the pure pro‐saccade task, the TS group were shown to be significantly slower to initiate and to complete the saccades (longer movement duration and decreased peak velocity) than controls, while movement amplitude and direction accuracy were not different. These findings demonstrate enhanced shifting ability despite slower reflexive responding in TS and are discussed with respect to a disorder‐related adaptation for increased cognitive regulation of behaviour.     

The Large Pursuit Rotor

The question of whether certain phenomena that occur on the conventional rotary pursuit and other small apparatus also appear on a gross motor task was examined using a large pursuit rotor that required whole-body movements. College males (n=29) were given 90 10-sec trials over three consecutive days with 30 trials of continuous practice per day. The existence of reactive inhibition, reminiscence, and warmup decrement was confirmed, indicating that common mechanisms underlie both fine and gross bodily movements. In addition, the substantial amounts of learning and the high reliabilities for performance and learning indicated that the present apparatus has considerable potential for motor-learning research.     

自主控制眼跳：实验范式、神经机制和应用

自主控制眼跳是眼跳类型之一。自主控制眼跳实验范式为研究各种脑损伤,神经疾病和精神失调提供了一种新的研究手段,为研究眼跳的神经机制以及反应抑制、空间工作记忆等高级认知功能提供了重要的方法。文章介绍了自主控制眼跳的两种实验范式：反向眼跳和记忆导向眼跳,阐述了自主控制眼跳的神经机制及其实验范式的应用,指出自主控制眼跳实验范式为评定精神分裂症等脑功能失调病人的神经功能状态提供了重要的信息,为研究各种脑功能失调和精神疾病提供了重要的研究方法。今后的研究趋势是眼跳研究与神经成像技术和临床观察相结合